For me, it has to be MW2.
It was the first COD I played and actually enjoyed (Played COD4 and W@W, didn't really like them at first), so I am speaking from nostalgia as well as my opinion, but I'll try to keep nostalgia out of it as much as I can.
Yes, MW2 has it's flaws. We all know them, we've talked about them to death. But the stuff that works, REALLY works. The maps are hands down my favorite in any COD game. If IW were to just release MW2 maps for the rest of the content drops for MW3, I'd be fine with that. The guns were the most balanced all around of any COD, bar one (UMP). Every gun had a pro and a con, not just pros or just cons like they have in BO/MW3. And to save you time, the ACR had low recoil but low damage. The SCAR had high damage and low recoil but a small clip and low ammo. See? Pros and cons. And the Tar-21 is by far my all time favorite gun of any COD. And even though the stopping power debate will go on for eternity, it made some guns that would be unusable without it pretty decent guns.
I liked all the little things too. Like the barrel roll with shotties or the knife flip.
But the thing that keeps me going back to MW2 to this day is the rambo effect. When I get going in MW2, I'm unstoppable. MW2 is set up so you can just go on a rampage and no one can stop you. Scavanger, Stopping Power, Ninja, Predator, Harrier, Chopper, Semtex, stun, AA-12, and your favorite gun, and you're gold. BO took the rambo effect and ****** it in the ass, and MW3 tried to bring it back, but there's so much BS in the game, it's just not the same. A streak in MW3 isn't as satisfying as a streak in MW2 for me. I feel like I just got lucky that I didn't get lag killed or I didn't fall victim to a bad spawn. In MW2, when I get going, I feel unstoppable because I know it's because of how I know the game and how I play it.
Even the flaws are starting to grow on me. Like when I'm getting destroyed by chopper right out of my spawn, I can't help but be a little charmed and think "only in MW2". That's the thing for me, "Only in MW2". There's so many things that are just in MW2 and I can't get anywhere else. Sure, some of it is bad, like commando, OMA/DC tubes, but I take the good with the bad. People forget how innovative MW2 was because most people just think of how bad it was. It introduced pro perks, increased the attachments, increased the killstreaks, etc. Blops and MW3 were built on the road that MW2 paved.
I can't help but wonder what would have happened to it if the fallout between IW and activision hadn't happened. Problems could've been fixed, more maps could've been made, just what could have been. But for what it is, I love it. It has a charm that will never be matched which is why even today, with over 17 days played on it, I still play.
